Production of bismuth



Feb. 5, 1935. J. o. BETTERTON Er AL v 1,989,734

PRODUCTION OF BISMUTH Filed oct. 8, 1932 INVENTORS fasse Q eeran/ ATTOR N EYS Patented Feb. 5, 1935 PRODUCTION 0F BISMUTH Jesse 0. Betterton and Yurii E. Lebedeff, Me-

tuchen, N. J., assignors to American Smelting and Rening Company, New York, N. Y., a corporation of New Jersey Application October 8, 1932, Serial No. 636,941

9 Claims. (Cl. 75-1!) This invention relates to the production of bismuth and provides a method for recovering bismuth metal from high bismuth bearing alloys of lead.

Heretofore it has been common and established commercial practice to recover bismuth from alloys of lead, containing appreciable quantities of bismuth, by oxidizing or chloridizing the lead and concentrating the bismuth as residual metal. However, these methods are not wholly satisfactory. in that the oxidation reaction is iarfrom selective, while the chloridization process is undesirable in cases where the bismuth lead alloy is high in lead.

By the present invention bismuth metal is recovered in an eiiicient manner from alloys of lead containing bismuth within an approximate range of 1.5% or somewhat less to 40% or above. In accordance with the present invention the high bismuth alloy is heated to a suitable temperature and magnesium incorporated therein, which resuits in the formation of a high bismuth-magnesium dross. The dross is then incorporated in a molten salt bath following which the bismuthsalt mixture is treated in an aqueous solution of a suitable reagent to dissolve the magnesium and accompanying salts. As a result the bismuth remains as a residue contaminated with more or less lead and is suitably smelted to obtain crude bismuth metal which may be treated by well known rening methods to procure high grade bismuth metal.

The drawing forming a part of the present specification is a flow sheet illustrating how the process of the invention may be practiced.

In practicing the invention a bismuth lead alloy, which may contain small quantities of other metals, such as gold, silver, arsenic, antimony and' copper, may be heated in a suitable kettle and the magnesium incorporated therein. A temperature oi approximately 650 F. to 750 F. is suitable for this purpose and it has been found that the upper limit should not be greatly exceeded if excessive oxidation losses of magnesium are to be prevented.

When the bath has been brought to the tembasket within the body of the bath. The pump and basket may be removed from the kettle when a proper amount of magnesium has been incorporated in the bismuth-lead alloy. If a leadmagnesium alloy is used, it may be readily 5 incorporated in the bath by directly adding the alloy to the molten bath, melting the alloy therein, and stirring the bath for a short period of time with an ordinary mixing machine.

Following the addition of magnesium to the 10 bismuth lead alloy the bismuth to be recovered as the nal product will form as a concentrated magnesium-bismuth dross which is removed from the bath and preferably pressed for the removal of lead therefrom. 'I'he latter may be accom- 15 plished by employing an ordinary Howard press, such as is commonly used in lead refining operations, and operating same at a desired working pressure of, say, 100 lbs. per square inch or higher.

To further illustrate the method of treating the bismuth lead alloy for the concentration of the bismuth as a dross used in the latter stages of the process and from which the bismuth metal is ultimately derived, the following two specific 25 examples are set forth:

Example 1 A molten bath of bismuth lead alloy, weighing 172 lbs. and analyzing 4.12% Bi, was established 30 in a cast iron kettle. The surface of the molten metal was then skimmed clean and 11.55 lbs of a magnesium lead alloy analyzing 12.09% Mg added to the bath which had a temperature of 690 F. After forty-ve minutes the alloy was completely melted, at which time the bath was stirred for three minutes with an ordinary mixing machine at a temperature of 685 F.

All of the dross formed was skimmed and pressed .by means of a small press operated by a hand screw which operation occupied approximately two hours and was carried on within a temperature range of the bath from 685 F. to 650 F. The pressed dross weighed 18.4 lbs. and analyzed 24.6% Bi which was approximately a six-fold concentration over the bismuth content oi the original alloy.

Example 2 Twelve tons of a bismuth-lead alloy analyzing 27.2% Bi was melted in a sheet steel kettle and metallic magnesium in ingot form was incorporated in the molten bath at a temperature of '130 F. The resulting dross was skimmed into a standard Howard press with the bath at a temperature of 650 F. and vpressed. The time for skimming and pressing was less than one hour and the pressed dross analyzing 39.0% Ei weighed 2400 lbs.

The bismuth to be recovered after concentration in the dross, and preferably after pressing as heretofore mentioned to remove part of the lead, is next mixed with suitable molten salts, that is, the higher halogen salts of the alkali, alkaline earth metals including magnesium. This may be accomplished by charging the concentrated bismuth dross into a kettle containing'molten calcium chloride and calcium iluoride, calcium chloride and magnesium chloride or other suitable salt mixtures. Sodium chloride may be added to the above or other mixtures if desired.

The kettle containing the bismuth-salt mixture is preferably provided with a heat insulating cover and should be heated to a temperature sumcient to practically melt the contents. Ordinarily, a temperature of approximately l300 F. or above is sufcient for this purpose. At this stage lead not previously removed will tend to liquate out and collect in the bottom of the kettle. A separation of this molten lead from the rest of the contents of the kettle may be eiected by any suitable means. For example, the cover may be removed and a pump inserted through the molten slag and mushy top layer of metal into the completely melted lead below. The contents of the kettle may then be cooled to approximately 950 F. to 1050 F. and the molten lead pumped out, thus leaving the frozen crust and slag in the kettle. This frozen crust is composed mainly of bismuth and magnesium in a form which is generally said to be a compound havingv the formula MgaBiz. A sample of such a crust analyzed 60% bismuth, magnesium and the balance lead.

After liquation and removal of the lead the kettle may again be covered and reheated to approximately 1400 F. which serves to remelt the crust and slag, after which the mixture may be removed from the kettle and cast in suitable molds. Alternatively, however, the bismuth-magnesium compound, after the lead separation, may be allowed to partially oxidize and with the frozen slag removed from the kettle as a powdery dross containing frozen slag crust.

The magnesium-bismuth-slag mixture may next be subjected to the dissolving action of water containing a suitable reagent such as sulphuric acid. As a result, all the constituents present except the bismuth and small amounts of lead pass into solution leaving as a residue the bismuth in a ne metallic or metal-like state consisting of metallic bismuth and lead or their oxides. 'I'his residue rapidly settles out after which time its separation may be eected, as by decantation. The residue may then be further washed with water to remove any of the original acid solution, and subsequently allowed to dry'.

The metal obtained as above set forth may then be Acharged to a suitable metallurgical furnace for smelting. As considerable oxidation may have resulted during the drying of the finely divided metal appropriate quantities of a suitable reducing fuel, such as coal or coke, should be thoroughly incorporated in the charge. The amountI of reducing fuel used should be carefully regulated so that the mixture when smelted will reduce the bismuth as crude metallic bismuth and leave the lead as molten litharge.' Lead may be recovered from the litharge in accordance with common lead smelting practice while the crude bismuth metal may be treated by any of the well known refining methods to produce chemically pure bismuth. Y f

While certain novel features of the invention have been disclosed and are pointed out in the annexed claims, it will be understood that various omissions, substitutions and changes may be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. The process of producing bismuth from a bismuth-lead alloy which comprises heating said alloy to an approximate temperature of 650 F. to 750 F., incorporating magnesium' therein thereby concentrating bismuth as a bismuthmagnesium-lead dross, pressing said dross to remove lead, mixing said pressed dross with salts of the class comprising higher halogen salts of alisali, alkaline earth metals including magnesium to form a salt-dross mixture and at a temperature suillcient to remove further quantities of lead by liquation, leaching the remaining saltdross mixture with water containing a small quantity of sulphuric Aacid to dissolve magnesium and soluble salts thereby obtaining. aL residue containing the bismuth content of the mixture,Y

washing and drying said residue, smelting same to recover crude bismuth and refining said crude bismuth.

2. The process of producing bismuth from a bismuth-lead alloy which comprises establishing a molten bath of such alloy, incorporating magnesium therein thereby concentrating bismuth in a dross, incorporating said dross in a molten salt bath comprising higher halogen salts of alkali, alkaline earth metals including magnesium to form a salt-dross mixture, treating said mixture with an aqueous solution of sulphuric acid to dissolve all the constituents of the mixture except bismuth and lead and smelting the high bismuth residue. n

3. In the recovery of bismuth from bismuthlead alloys the improvement which comprises concentrating bismuth as a bismuth-magnesiumlead dross, incorporating said dross in a suitable salt bath comprising chlorides and/or fiuorides of alkali, alkaline earth metals including magnesium at a temperature of approximately 1300 F., cooling said bath to a temperature of approximately 950 F to 1050 F., separating lead therefrom, reheating the bath to approximately 1400 F. and subsequently leaching the salt-dross mixture with an aqueous solution of sulphuric acid for the recovery of bismuth as a finely divided residue. ,l

4. The. method of producing bismuth from a bismuth-lead alloy having a bismuth content of approximately 1.5% to 40% which comprises establishing a molten bath of such alloy at a temperature'of 650 F. to 750 F., incorporating magnesium therein to concentrate bismuth as a dross, pressing said dross to remove lead, formalloy to an approximate temperature of 650 F. 75

to '150 F., incorporating magnesium therein thereby concentrating bismuth as a bismuthmagnesium-lead dross, pressing said dross to remove lead, mixing said pressed dross with suitable salts of the class comprising higher halogen salts of alkali, alkaline earth metals including magnesium to form a salt-dross mixture and at a temperature suilicient to remove further quantities of lead by liquation, and recovering finely divided bismuth from the remaining salt-dross mixture by leaching with a reagent capable of dissolving magnesium and accompanying salts.

6. In the recovery of bismuth from bismuthlead alloys the improvement which comprises concentrating bismuth as a bismuth-magnesiumlead dross, incorporating said dross in a suitable salt bath comprising chlorides and/or iluorides of the alkali, alkaline earth metals including magnesium, separating lead therefrom, allowing the remaining mixture to partially oxidize and leaching same thereby obtaining bismuth contaminated with small amounts of lead as a iinely divided and partially oxidized residue.

7. In the recovery of bismuth from bismuthlead alloys the improvement which comprises concentrating bismuth as a bismuth-magnesiumlead dross, incorporating said dross in a suitable salt bath comprising halogen salts of alkali, alkaline earth metals including magnesium at a temperature of approximately 1300 F., separating lead therefrom, reheating the bath to a temperature of approximately 1400 F. to form an intimate salt-dross mixture and treating same with water containing sulphuric acid in quantities sumcient to dissolve the magnesium and soluble salts and recovering bismuth as a residue.

8. The process of producing bismuth from a bismuth-lead alloy which comprises heating said alloy to an approximate temperature of 650 F. to 750 F., incorporating magnesium therein thereby concentrating bismuth as a bismuthmagnesium-lead dross, pressing said dross to remove lead, mixing said pressed dross with halogen salts of the alkali, alkaline earth metals including magnesium to form a salt-dross mixture and at a temperature sui'iicient to remove iur-4 ther quantities of lead by liquation, leaching the remaining salt-dross mixture with water containing a small quantity of sulphuric acid to dissolve magnesium and soluble salts thereby leaving a residue containing the bismuth content of the mixture, washing and drying said residue and smelting same thereby recovering crude bismuth.

9. In the recovery of bismuth from bismuthlead alloys, the improvement which comprises concentrating bismuth as a bismuth-magnesiumlead dross, incorporating said dross in a suitable salt bath of higher halogen derivatives ot the alkali, alkaline earth metal groups at a temperature. of approximately 1300 F., separating lead therefrom, partially oxidizing the salt-dross mixture and separating iinely divided bismuth therefrom by selectively dissolving the magnesium and accompanying salts.

JESSE 0. BE'I'IERTON. YURII E. LEBEDEFF. 

